High prevalence of p16 genetic alterations in head and neck tumours

Inactivation of the p16 gene is believed to contribute to the tumorigenic process of several neoplasms, including head and neck tumours. In the present study, DNA samples from paired tumour and adjacent normal tissue from 47 patients with squamous cell carcinoma of the head and neck were investigated for the occurrence of p16 genetic alterations. Single-strand conformation polymorphism and direct DNA sequence analysis led to the identification of p16 mutations in six cases (13%). Southern blot analysis showed that homozygous deletion is a rare event in the group of tumours analysed. Loss of heterozygosity (LOH) analysis was performed by polymerase chain reaction (PCR) using two microsatellite markers (IFNA and D9S171) from the 9p21 region. Taking into account only the informative cases, 17 of 32 tumours (53%) showed LOH for at least one of the markers analysed. The methylation status of the CpG sites in the exon 1 of the p16 gene was analysed using methylation-sensitive restriction enzymes and PCR amplification. Hypermethylation was observed in 22 (47%) of the head and neck tumours analysed. In our series of head and neck tumours, evidence for inactivation of both p16 alleles was observed in 13 cases with hypermethylation and LOH, two cases with hypermethylation and mutation, four cases with mutation and LOH and one case with homozygous deletion. These findings provide further evidence that genetic alterations, especially hypermethylation and LOH, leading to the inactivation of the p16 tumour suppressor gene are common in primary head and neck tumours.